For example, Japanese Patent Application Number P2001-208843 A published on Aug. 3, 2001 discloses an obstacle detection system that includes four ultrasonic sensors and a controller. Each ultrasonic sensor includes a microphone, a transmission circuit, an attenuator circuit and an amplifier circuit. The microphone is configured to emit and receive ultrasonic waves. The transmission circuit is configured to drive the microphone in accordance with control of the controller. The attenuator and amplifier circuits are configured to adjust a level of a signal obtained from incoming ultrasonic waves.
The obstacle detection system is configured so that one ultrasonic sensor of a plurality of (four) ultrasonic sensors emits ultrasonic waves and other ultrasonic sensor then receives incoming ultrasonic waves obtained from the ultrasonic waves. This leads to expand a maximum detection area covered with the plurality of ultrasonic sensors.
The obstacle detection system is also configured to adjust a level of a signal obtained from incoming ultrasonic waves so that a detection area is changed to a short distance area or a long distance area and a beam angle for the long distance area (especially, a vertical beam angle) is smaller than a beam angle for the short distance area. This leads to prevent a false detection caused by a small projection of a road surface, or the like.
The obstacle detection system however requires that the four ultrasonic sensors be mounted on a bumper fixed to a vehicle, for example, at 50 cm intervals.